In the future mobile communication system, such as: in B3G (Beyond Third Generation) or LTE-A (Long Term Evolution Advanced), higher peak value data rate and cell throughput will be provided, and wider bandwidth is needed at the same time, at present, there is little unallocated bandwidth below 2 GHz, part of or the whole bandwidth for B3G system can only be at higher frequency channel, for example, above 3 GHz. However, the higher frequency channel is, the faster attenuation of radio propagation and the shorter transmission distance will be, thus, in the same coverage area, more base stations are needed to guarantee continuous coverage, and network laying cost will be undoubtedly increased due to high construction cost of base station.
In order to solve network laying cost and coverage problem, manufacturers and standard organizations start to introduce Relay Node (RN) into cellular system to increase coverage.
FIG. 1 is the diagram of network architecture after RN is introduced into LTE-A system in prior art, RN is linked to core network through donor cell under evolved Node B (eNB), while RN itself and core network don't have direct wired interface, each RN can control one or several cells. Under this architecture, interface between User Equipment (UE) and RN is called Uu interface, and that between RN and DeNB is called Un interface.
To be specific, RN in the abovementioned architecture is featured with double identities:
(1) Firstly, RN is featured with the ID of UE, start of RN is similar to attach procedure in start of UE. RN has its own SGW (Serving Gateway)/PGW (Packet Data Network Gateway) and Mobility Management Entity (MME).
(2) Secondly, for UE connected to RN, RN is featured with the ID of eNB, and now downlink data of UE is required to be sent to service base station of UE (Via RN) from UE's own SGW/PGW, and sent to UE by RN at Uu interface.
FIG. 2 is the flow diagram of start procedure of RN in prior art, corresponding start procedure of RN can be described as below:
RRC connection is set up between RN and DeNB; RN sends attach request to MME; MME acquires authentication vector from HSS (Home Subscriber Server) and conducts authentication on RN; if authentication is passed, MME will set default bearer in SGW/PGW for RN, send initial context to DeNB (Donor evolved Node B) to set up request message, thus to set up context for access layer of RN in DeNB; DeNB sends RRC (Radio Resource Control) connection reconfiguration complete message and attach acceptance message sent to RN by MME to RN afterwards; RN returns to RRC connection reconfiguration to finish confirmation. In this way, RN sets up basic IP (Internet Protocol) connection.
Then O&M (Operation and Maintenance) equipment will download node configuration information to RN and conduct configuration on RN. RN can be in normal operation like base station after setting up necessary S1 interface and X2 interface.
Furthermore, FIG. 3 is the flow diagram of detach of RN from network in prior art, corresponding RN shutdown procedure can include detach procedure of RN as a regular UE from network as well as configuration update procedure towards neighbor eNB initiated by DeNB.
Furthermore, FIG. 4 is the structure diagram of MBMS (Multimedia Broadcast Multicast Service) system architecture in prior art. M1 interface refers to a pure user plane interface defined between eNB and MBMS GW, the interface provides unguaranteed user plane data transmission between MBMS GW and eNB. M2 interface refers to a control plane interface defined between eNB and MCE (Multi-cell/Multicast Coordination Entity), the interface is mainly used for MBMS session management function and MBMS scheduling information supply function. M3 interface refers to a to control plane interface defined between MME and MCE, the interface is mainly used for MBMS session management function.
In the procedure of implementing the embodiments of the present invention, at least the following problems existing in the current technologies were found:
In prior art, a regular eNB can control all or part of cells under control of eNB to participate in transmission of MBMS service based on scheduling information of MCE. However, if hybrid deploy scene of RN and regular eNB in network is considered, on one hand, RN doesn't support transmission of MBMS, on the other hand, major deploy scene of RN is used for expanding coverage (in expanded coverage area, UE can only receive signal from RN), thus, once UE is moved to RN coverage area, UE will not continue to receive MBMS service normally, which will seriously influence user experience.